Acantopsis ioa, Boyd & Nithirojpakdee & Deein & Vidthayanon & Grudpan & Tangjitjaroen & Pfeiffer & Randall & Srisombat & Page, 2017

Boyd, David A., Nithirojpakdee, Patchara, Deein, Gridsada, Vidthayanon, Chavalit, Grudpan, Chaiwut, Tangjitjaroen, Weerapongse, Pfeiffer, John M., Randall, Zachary S., Srisombat, Tippamas & Page, Lawrence M., 2017, Revision of the horseface loaches (Cobitidae, Acantopsis), with descriptions of three new species from Southeast Asia, Zootaxa 4341 (2), pp. 151-192 : 179-182

Acantopsis ioa new species, Boyd and Page

Slender Horseface Loach

( Fig. 19 )

Holotype. UMMZ 250301 , 128.4 mm SL (ex. UMMZ 240684 ), Laos, Mekong River drainage, Vientiane Province, Nam Lik, 6 km upstream of confluence with Nam Ngum River , 18.583N, 102.500E , 22 January 1997, W. J. Rainboth and M. Anderson.

Paratypes. Laos: Mekong River drainage: UMMZ 240684 (13, 88.4–132.0 mm SL), same locality and date as holotype . UF 190865, 3, 96.5–114.9 mm SL (ex. UMMZ 240684). THNHM F0013612, 1, 107.1 mm SL (ex. UMMZ 240684). Thailand: Mekong River drainage: UF 188135 (23, 60.6–98.4 mm SL), Ubon Ratchathani Province, Khong Chiam District, Mekong River at mouth of Mun River , 15.318N, 105.513E, 22 January 2015, D . Gridsada et al.; ANSP 200532 (2, 78.8–79.0 mm SL), ex . UF 188135; NIFI 5103 (2, 72.2–73.3 mm SL), ex. UF 188135; ZRC 55597 (2, 80.2–82.8 mm SL), ex. UF 188135; INHS 110605 (2, 82.7–83.6 mm SL), ex. UF 188135.

Diagnosis. Acantopsis ioa differs from all other species of Acantopsis ( Table 4) by combination of no labial barbels, usually no distinct small black spot on upper margin of caudal-fin base, 0–1 row of large spots on side of head, no large black spots on dorsal or caudal fins, no row of black specks beneath midlateral row of black spots, usually 9½ branched dorsal rays and 10 pectoral rays, 15–23 narrow, blotch-like saddles along dorsal midline, 13– 21 black spots along side of body, and 46–48 total vertebrae, body depth 8.5–11.0% SL, body width 5.2–7.9% SL, caudal-peduncle length 13.1–16.2% SL.

Comparisons. Acantopsis ioa is distinguished from all species of Acantopsis by having narrow blotch-like dorsal saddles, 46–48 (vs. <45) total vertebrae ( Fig. 15 ), and from all other species in the genus except A. rungthipae by having no labial barbels. It is further distinguished from A. rungthipae by usually lacking a distinct small black spot on upper margin of caudal-fin base, 13–21 (vs. 9–17) black spots along side of body. It further differs from A. dinema in having no black specks beneath midlateral row of black spots, large dark spots usually present on side of head, usually 9½ (vs. 10½) branched dorsal rays, smaller body depth (8.5–11.0 vs. 12.0–14.5% SL) and width (5.2–7.9 vs. 8.0–10.2% SL). It further differs from A. octoactinotos in having no distinct small black spot on upper margin of caudal-fin base, large dark spots usually present on side of head, usually 9½ (vs. 8½) branched dorsal rays, usually 10 (vs. 9) pectoral rays. It further differs from A. spectabilis and A. thiemmedhi in lacking conspicuous black spots, blotches, or bands on caudal, anal, and paired fins and in having 15–23 (vs. <13) dark saddles along dorsal midline, from A. thiemmedhi in lacking a large black blotch on the tip of the anterior rays of the dorsal fin and in having usually 9½ (vs. 10½) branched dorsal rays, and from A. dialuzona by lacking a well developed ocellus on upper margin of caudal-fin base and having usually 9½ (vs. 10½) branched dorsal rays.

Description. As in description of genus; Tables 1, 2, 4. Head long (21.8–24.2% SL); snout long (61.0–69.6% HL); no exposed labial barbels; 9½, rarely 10½, branched dorsal rays; 10, less often 9 or 11, pectoral rays; 33–35 abdominal plus 13–14 caudal = 46–48 total vertebrae. Maximum SL = 132.0 mm, TL = 152.9 mm (UMMZ 240684).

Color. Dark spots in 1 or 2 rows on top of head. Few large dark spots on side of head; if present, usually in 1 row. Faint line from eye to tip of snout. Fifteen–23 narrow, rounded saddles along dorsal midline; 13–21 dark spots along lateral line from head to caudal fin; spots more discrete than in other species. Small dark spots on upper side of body; no dark spots on lower side of body. Dorsal and caudal fins with faint bands; other fins without bands. Often a dusky stripe on lower margin of caudal fin. No small bold black spot (rarely present) or ocellus near upper margin of caudal-fin origin.

Etymology. The epithet ioa , from Greek for an arrow or dart, refers to the relative slenderness of this species in relation to other species of Acantopsis .

Distribution. Acantopsis ioa is widespread in the mainstem Mekong River in Thailand and Laos ( Fig. 20 ). It also is known from the Nam Lik, a large tributary of the Mekong in Laos, and the Srepok River, a large tributary of the Mekong in Cambodia.

Figures

FIGURE 15. CT-scans of (A) Acantopsis rungthipae, THNHM F 0013610, holotype, 107.4 mm SL. (B) A. dinema, THNHM F 0013611, holotype, 100.7 mm SL. (C) A. ioa, UF 188136, 95.5 mm SL. CT-scans proVided by E. L. Stanley (UF).

FIGURE 19. Acantopsis ioa. (A) Lateral VieW, UMMZ 250301, holotype, 128.4 mm SL. (B) Lateral and dorsal VieWs, UMMZ 240684, paratype, 131.0 mm SL.

FIGURE 20. Localities of specimens examined of Acantopsis ioa.